Camera Tracking markers
With the new affine/perspective tracking you can get much better tracking by having a marker that has some features within it. Here's a brief hierarchy of how I think about what makes a good tracking marker:


Bare Minimum:
Some kind of point you can track the position of. Vulnerable to being lost due to noise. Can't track scale or rotation very well.


Better:
A corner gives you more to track, and is less likely to get lost, but can disappear it the camera moves too much around the object, and you probably can't track it's scale.


Best:
Some kind of small pattern or grouping of features. This gives you something with high contrast that you can also keep track of the rotation and scaling of with the Perspective motion model. This should give you a more robust track and thus a better camera solution.